Sound producing device



Ma 17, 1938. J, c ow 2,117,903

SOUND PRODUCING DEVICE Filed Sept. 12, 1936 Fig. 4. m" 5? 4 I 5 Inventor:

Albert J. Muchow; A A z 1 )Vwy'J Pressure I Patented May 17, 1938 UNHTED STATES PATENT GiFliZE SOUND PRODUCING DEVICE York Application September 12, 1936, Serial No. 100,519

Claims.

The present invention relates to a novel sound producing device adapted for use as a secondary standard of sound intensity in calibration operations. More particularly, the invention relates 5 to a whistle having unusual characteristics of a nature to be described more completely in the following.

It is a normal characteristic of whistles and similar devices that as the pressure of the enerl0 gizing fluid (normally air) is increased, a point of maximum sound intensity output is reached above which a further increase in pressure produces a decrease or cessation of sound output due to the phenomenon known as overblowing. It is characteristic of most whistles of prior construction that as the boundary of overblowing is approached the sound output becomes unstable or wabbly so that the production at will of a note of definite intensity is extremely difiicult with such whistles.

It is an object of the present invention to provide a whistle of such construction that its output .aall be stable up to the region of overblowing and shall cut off very definitely at the boundary of that region.

It is a further object to provide a whistle of the above stated nature whose performance shall be dependably reproducible from time to time and by diiierent users and whose output shall be only 39 negligibly affected by temperature and other variconditions encountered in practical use.

In the attainment of these objects I aim to make available a reliable standard of sound insity which is cheap, readily portable, and easily 35 maintained in proper adjustment.

In the preferred embodiment the invention comprises an elongated resonating tube which is provided with a restricted outlet orifice at one end thereof and which merges abruptly at its 0 other end into a relatively enlarged chamber. By supplying air at regulated pressure to the latter one may produce a whistling note, the frequency of which is dependent in part on the length of the resonating tube and in part on the pressure at which air is supplied. The variations in frequency and intensity of sound output due to this latter factor are not continuous as m be expected but are more or less abrupt, taking the form regions of relatively constant and stable output alternated with regions of zero sound production. The theoretical reasons for this mode of operation are at present not fully understood, but, as will be shown in the following, the results obtained are such as to impart unusual utility to a whistling device constructed in the manner specified.

The novel features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself together with further objects and advantages thereof may best be understood with reference to the following specification taken in connection with the accom-- panying drawing in which Figs. 1 and 2 show in perspective and in section respectively the d tails of construction of my improved whistle; 3 illustrates graphically ce tain aspects of performance of the whistle, and Fig. 4 is a f agmentary section showing an enlarged view of the outlet orifice.

Referring particularly to Fig. l, I have shown therein a whistle constructed accordance with my invention. This whistle comprises a resonating chamber 1 preferably comprising an elongated metal tube the length of which is determined by the frequency desired to be produced by the whistle. The outlet end of the resonating chamber l is in the case illustrated covered by a. cap member 3 comprising a restricted orifice 4 and provided with a laterally projecting gauge member 5, the purpose of which wiil be more fully hereinafter.

I have found that under certain conditions if air is blown into the end of the resonating remote from the orifice 4, a definite whistling effect can be obtained. It is thought that the direct cause of the whistling is the turbulence or fluttering set up in the air stream at the outlet orifice. This fluttering is apparently reinforced and amplified by resonant acoustic oscillations occurring in the resonating tube. It is true at any rate that the Whistling frequency is a function of the resonating tube length.

Most perfect operation of a resonating tube of the type described will be obtained if the inlet end of the tube is entirely unobstructed and is open to the surrounding atmosphere. In actual use, however, this condition is impractical to cbtain since any attempt to introduce the encrgizing air stream from a distance results in a con? siderable waste of air and further permits reflection of sound from the open end of the tube, which sound interferes objectionabiy with the fundamental note issuing from the or fice ii. In

order to overcome these disadvantages in a man- F ner which still allows effective operation of the resonating tube in the desired manner, chamber I is provided at its inlet end with an enlarged chamber comprising a hollow cylinder I. This is partially closed at the end nearest the resonating tube by a plane transverse wall 8 having a central opening 9 of at least as great a diameter as the diameter of the tube. I have found that for best results the diameter of the cylinder i should be considerably in excess of that of the tube 5 and that the transition between the cylinder and the tube should be an abrupt one as is in fact provided by the wall 8.

For introducing air or a similar energizing medium into the chamber i, a long tube or conduit l is provided which opens into the end of the chamber remote from the central opening 9. At the extreme end of this conduit is mounted a mouth-- piece consisting of an enlarged cup-like member it which is given this particular form for sanitary reasons. I do not consider that the position or dimensions of the conduit H are essential to my invention, and the rigid conduit illustrated may, if desired, be replaced by a flexible connecting means.

In a particular whistle constructed in accordance with my invention, a resonating tube is employed having an overall length of about five and three-sixteenths inches (5 and an internal diameter of nine-sixteenths of an inch (5%). In the same whistle the enlarged chamher is about two inches (2) long and one and three-eighths inches (1%") in internal diameter, while the outlet orifice is about one-quarter inch /4) across and is formed in a wall member one-sixteenth inch thick. With these dimensions the whistle emits a note of approximately one thousand cycles frequency, or under certain conditions a multiple thereof. It should be understood, however, that the values given in the foregoing are exemplary and not limiting and that greater or smaller dimenisons may be employed if desired.

The characteristics of a whistle such as that described in the foregoing are, as far as I am aware, entirely unique. As the pressure of the energizing air stream is gradually increased, the transition from a soundless to a sound-producing condition is very abrupt as is indicated in Fig. 3. This figure illustrates the relation between sound intensity produced by the whistle plotted as ordinates and applied fluid pressure plotted as abscissa. Thus at a pressure represented by the point A the intensity of sound output rises from zero to a sound of intensity B, which sound has a frequency determined by the length of the resonating tube As the pressure is still further increased, an additional increase in intensity is noted which reaches a maximum at a point C. Above this point any additional increase in pressure results in a substantially immediate cessation of sound, such cessation being very definite and free from any indication of unsteadiness. Because of this fact, the point C may be very readily located by the operator and can be reliably reproduced by a number of different operators. Accordingly a whistle of the type specified is ideally adapted to be used as a standard of sound intensity.

I have observed that the sound produced in the region from B to C is of approximately constant .irequency. However, as the pressure increases above the first region of overblowing, another pressure represented by point D will be reached at which the whistle emits a note which is a harmonic of the first frequency, Furthermore, if the p" ssure is still further increased to that represented by a fourth point E, still another harmonic may be obtained. Either the even or the odd harmonics may be selectively eliminated,

and the whistle made more reliable in use by providing a vent in the wall of the resonating tube at a properly chosen point. Thus a vent 6 placed at approximately the center of the tube will inhibit the fundamental and its odd harmonics, while a vent 8 placed about a quarter of the way from the end of the tube will prevent even harmonics. It will be understood, of course, that only one vent may be open at a time if any sound output is to be realized.

The definiteness of cut-off as well as the intensity of output of a given whistle are affected considerably by the configuration of the outlet orifice, and in Fig. 4 I have illustrated the particular configuration which I consider to give best results. In this figure it will be noted that the lip of the orifice 4 which is adjacent the inner side of the wall 3 is slightly beveled. The nature of the bevel which will give optimum operation should be determined experimentally for each whistle size. By way of example, it may be stated that when the thickness of the wall 3 is about inch and the diameter of the orifice is about inch, the width of the beveled region It should be about /64 of an inch, and bevel being inclined at an angle of about 45 degrees with respect to the central axis of the whistle.

The manner of use of my improved whistle as a standard of sound intensity in calibration oper ations is illustrated diagrammatically in Fig. 22.

In this figure the numeral l'l indicates the dotted outline of a microphone or corresponding input element of the apparatus which is to be calibrated. For insuring consistent results, the whistle as a whole is so positioned that the tip of the gauge 5 just touches the outside of the microphone. Under these conditions the orifice 4, which constitutes for all practical purposes a point source of sound, will be at a definite predetermined distance from the microphone. Consequently, any number of different operators following the same procedure will be able to obtain highly consistent results.

Whistles constructed in accordance with my invention are of utility in the calibration of radio broadcasting equipment and sound level meters and an intercomparison of sound standards. Since these Whistles are readily portable, easily cleaned and contain no moving parts to get out of adjustment, they may advantageously replace the more complex and costly sound generating equipments which have heretofore been used for sound intensity calibrations.

By combination with suitable auxiliary equip ment, whistles of the type described may also be used as oral monitoring devices for indicating variations of fluid pressure from a value which it is desired to maintain. In this latter application the whistle should be so designed and so connected to the fiuid system under observation that the desired pressure will correspond. to a range of zero output (overblowing) of the whistle. Accordingly, any variation in pressure above or below this range will cause the whistle to produce a note whose frequency is determined by the direction of the variation.

While I have described my invention in connection with a particular structural embodiment thereof, it will be understood that many modifications may be made by those skilled in the art without departing from the invention, and I aim in the appended claims to cover all such equivalent structures as come within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:-

1. A whistle comprising a hollow cylinder, an inlet for air at one end of said cylinder, a plane transverse wall partially closing the other end of said cylinder, an elongated hollow tube of substantially smaller diameter than said cylinder communicating with the cylinder through an opening in said transverse wall, the opening in said wall being of at least as great a diameter as the diameter of said tube, and means comprising a restricted orifice partially closing the end of said tube remote from said cylinder.

2. A standard of sound intensity adapted to be used in calibration operations, said standard comprising a whistle having a resonating tube providing with a restricted orifice afi'ording a substantially point source of sound, and means associated with said whistle for accurately positioning the same with respect to the sound input element of an apparatus which is to be calibrated.

3. In a whistle adapted to serve as a standard of sound intensity in calibration operations, a resonating tube, and a member operatively connected to the outlet end of said tube, said member comprising a restricted discharge orifice forming a substantially point source of sound and a gauge element projecting laterally from said member for accurately positioning said element with respect to the sound input element of an apparatus which is to be calibrated.

4. A standard of sound intensity adapted to be used in calibration operations, said standard including a resonating tube provided with a restricted orifice for afiording a substantially point source of sound, means for introducing air or a similar energizing medium into the resonating tube, and a gauge element associated with the resonating tube adjacent to the orifice for facilitating accurate orientation of the orifice with respect to the sound input element of an apparatus which is to be calibrated.

5. A whistle comprising a hollow chamber, a resonating tube having one end thereof abutting against a wall of the chamber and communicating with the chamber through an opening in such wall, the said wall being approximately normal to the axis of the tube in the region surrounding the opening whereby the transition from the tube to the chamber is an abrupt one, means providing a restricted orifice at the end of the tube more remote from the chamber, and means for supplying air to the tube through said chamber.

ALBERT J. MUCHOW. 

